The present invention relates to the field of radiotherapy devices, and more particularly to the field of implantable, permanent or retrievable radiotherapy devices. More particularly still, the present invention relates to the field of shielded radioactive wires adapted for implantation at the site of a lesion or other selected body tissue for treatment of cancer or other pathological condition.
At present, external beam radiotherapy is widely utilized in the treatment of cancer and more recently, in the treatment of vascular malformations particularly those affecting the Central Nervous System. Radiotherapy is used as an adjunct to surgical excision and chemotherapy, or as the sole form of treatment.
External beam radiotherapy can be either nonfocused or stereotactic using a gamma knife apparatus or a linear accelerator. Both of these radiotherapy modalities are limited by the undesirable side effect of radiation necrosis they produce in the normal tissue surrounding the lesion to be irradiated.
Interstitial brachytherapy is a form of therapy which delivers local radiation to a lesion using permanent implants (seeds) which are surgically inserted in or very close to the area of interest. Theoretically, brachytherapy allows the delivery of a high dose of radiation to the abnormal or cancerous tissue with minimal or limited damage to the adjacent normal structures. Interstitial brachytherapy is often utilized to supplement surgical excision of a tumor or in combination with external beam radiotherapy. The permanent implants used in interstitial brachytherapy are inserted in the tumor bed during direct surgical exposure or utilizing a stereotactic localization device.
It would be desirable to provide a brachytherapy device that can be inserted percutaneously in cancerous lesions or vascular malformations through a microcatheter introduced in the body via the arterial tree, the venous system, or any other physiologic collecting or drainage ductal system. This would provide a relatively simple, cost effective, and medically effective treatment which would also be relatively easy to implant in the patient""s body. Using a procedure of this type would in most cases be less traumatic to the tissues involved, and would thus be less risky than traditional methods of interstitial brachytherapy. In addition, it would be desirable to provide such a brachytherapy device that can be retrieved and replaced if necessary or desired, or left permanently in place.
Presently, there are several types of embolic devices available which can be introduced in the arterial or the venous system through a microcatheter. One such device is in the form of a thin metallic coil or a thin composite metallic wire that can be preloaded in a polyethylene sheath and introduced percutaneously into the area of interest through the microcatheter. This known device can be delivered using a controlled delivery mechanism or simply injected through the catheter.
The embolic devices referred to in the previous paragraph are currently used for their thrombogenic effect to occlude blood vessels. It would be advantageous to use such known systems not only for such purposes, but also for the dual purpose of an implantable radiation device. This way, the simple, effective delivery systems now known for thrombogenic treatments can also serve as radiotherapy delivery systems.
The radiotherapy device of the present invention comprises a wire of radioactive material which is designed and adapted to deliver an intended dosage of radiation to a lesion or other selected body tissues. The wire of radioactive material preferably comprises an inner core about which is disposed an outer buffer layer of platinum or other suitable metal of high atomic number. The outer buffer layer may comprise a relatively thin, continuous wire of round, flat, or other suitable cross-section, wrapped in spiral or helical fashion about the inner core, and is adapted to attenuate the radiation. The radiotherapy device of the present invention may be made into a variety of shapes or configurations depending, for example, on the anatomy of the vessel or ductal system or other body tissue where the device will be inserted or used. For example, the device may be shaped into a straight wire, or it may be formed into a helical coil or coils or other more complex shape. The device may be provided with an elastic memory whereby it has a helical or other desired shape in the relaxed state, but may be inserted into the tissue, vessel, or the like in a straightened configuration; and then when released or inserted into the treatment site, it may resume or regain its original, relaxed (e.g., helical) shape.
The radiotherapy device of the present invention may be adapted for attachment to a delivery wire for controlled placement, as through a catheter or microcatheter disposed over a guide wire, at the intended treatment site. The delivery wire and the radiotherapy device of the present invention are preferably sufficiently radiopaque so as to enable easy fluoroscopic visualization in the insertion or delivery process. When accurate positioning of the radiotherapy device of the present invention is not necessary, it can simply be injected through the delivery catheter or microcatheter. In the latter event, a delivery wire is not needed.
The radiotherapy device of the present invention may be provided with mechanically or electrically releasable means for attaching the device to the delivery wire during the delivery process, and for releasing the device at the treatment site to allow removal of the delivery catheter and guide wire, thus leaving the radiotherapy device present at the treatment site either permanently or for later retrieval. With regard to electrically releasable attachment means, a soldered connection between the delivery wire and the radiotherapy device of the present invention may be released through electrolysis by application of a small direct current to the joint. A mechanically releasable attachment means for the radiotherapy device of the present invention may comprise a pair of interengaging hooks disposed, respectively, on the distal end of the delivery wire and the proximal end of the radiotherapy device.
The radiotherapy device of the present invention may be used as a permanent implant, or alternatively, it can be adapted to permit retrieval and replacement. A retrievable embodiment of the radiotherapy device of the present invention includes a head having a shoulder, hook, or the like on its distal end which may be lassoed by a microsnare device, again delivered through a microcatheter or the like, and easily pulled from the body through the same microcatheter.
These and other objects and advantages of the invention will become apparent from the following description of the preferred embodiment when read in conjunction with reference to the following drawings, wherein: